Wear-resistant stainless steel

ABSTRACT

Austenitic stainless steel characterized by workability, weldability and resistance to wear. The steel contains the three essential ingredients chromium, nickel and silicon, with one or more of molybdenum, tungsten, vanadium, columbium/tantalum and titanium, and remainder iron. The chromium amounts to about 10 percent to 22 percent, nickel about 14 percent to 25 percent, silicon about 5 percent to 12 percent especially about 7 percent to 11 percent, together with about 3 percent to 12 percent of the group consisting of molybdenum up to 10 percent, tungsten up to 8 percent, vanadium up to 5 percent, columbium/tantalum up to 5 percent and titanium up to 5 percent. The carbon content should not exceed about 0.15 percent. Copper may be present in amounts up to 5 percent. The steel is particularly suited to applications in the food-processing, the petro-chemical and the nuclear industries, where sliding or relatively moving parts are encountered. It also is suited to the production of cutting tools and surgical instruments.

I United States Patent [151 3,663,215 Tanczyn 1 May 16, 1972 [54] WEAR-RESISTANT STAINLESS STEEL Primary ExaminerHyland Bizot [72] Inventor: Harry Tanczyn, Baltimore, Md. Attorney-10m Howard Joynt {73] Assignee: Armco Steel Corporation, Middletown, [57] ABSTRACT 011' lo Austenitic stainless steel characterized by workability, welda- [22] Filed: Aug. 13, 1969 bility and resistance to wear. The steel contains the three es- [211 PP No: 849,861 sential ingredients chromium, nickel and silicon, with one or more of molybdenum, tungsten, vanadium, columbium/tantalum and titanium, and remainder iron. The chromium [52] US. Cl ..75/128 C, 75/128 W, 75/128 Z, o t to about 10 percent to 22 percent, nickel about 14 75/128 V percent to 25 percent, silicon about 5 percent to 12 percent [5 especially about 7 percent to l percenh together ith about [58] Field of Search ..75/123 Cl, 128 R 3 percent to 2 percent f the group Consising f molyb. denum up to 10 percent, tungsten up to 8 percent, vanadium [56] References C'ted up to 5 percent, columbium/tantalum up to 5 percent and UNITED STATES PATENTS titanium up to 5 percent. The carbon content should not exceed about 0.15 percent. Copper may be present in amounts 1,790,177 l/l931 Stoody ..75/128 R up to 5 percent. The steel is particularly suited to applications 3,198,631 8/1965 Jones ..75/128 R in the fogd-processing, the petro-chemica] and the nuclear in. 3,235,417 2/1966 W dustries, where sliding or relatively moving parts are encoun- 3,044,871 R tered. It also is suited to the production of cutting tools and 3,476,555 7/1969 Kohl ,.75/128 R i l instruments 2,984,563 5/1961 Tanczyn ..75/128 C 9 Claims, No Drawings WEAR-RESISTANT STAINLESS STEEL In introduction, my invention generally relates to the austenitic stainless steels.

One of the objects of the invention is the provision of an austenitic chromium-nickel stainless steel which by reason of the addition of other ingredients in particular amount is of exceptional cleanliness, and not only is workable and/or machinable, but is of great hardness and strength and especially suited to applications where there is encountered a combination of corrosive attack and frictional wear.

Another object is the provision of a steel of the character indicated which may be converted from billet and bar into plate, sheet, strip, bar, rod and wire forms by conventional mill practice which may be fabricated by a brazing or by a welding technique, and which may be cut, drilled, tapped, threaded and otherwise machined in the production of a host of articles of ultimate use.

A further object is the provision of an austenitic chromiumnickel stainless steel of the general character indicated which is suited to food-processing, petro-chemical and nuclear applications, as well as applications on the farm, in industry, and in the home.

Other objects of my invention in part will be obvious from the description which follows and in part particularly pointed to hereinafter.

BACKGROUND OF THE INVENTION As an aid to a better understanding of certain features of my invention, it may be well to note at this point that the austenitic chromium-nickel stainless steels are well known in the art. These generally may be viewed as stainless steels containing some percent to 30 percent chromium, with nickel on the order of some 3 or 4 percent on up to about 30 or 35 percent. One such austenitic steel which is suited to a variety of applications where welding is required and which also lends itself to applications in the chemical and food-processing industries is the A151 Type 304 (18-20 percent chromium, 8-12 percent nickel, 0.08 percent max. carbon, 2.00 percent max. manganese, 1.00 percent max. silicon, and remainder iron). The low-carbon modification of this steel, the A181 304L, is of like composition except the maximum carbon content is 0.03 percent. This steel is particularly suited to applications where the steel is to be used in the as-welded condition. Unfortunately, neither the Type 304 nor the Type 3041. is suited to applications where wear and abrasion are encountered under stress, the metal frequently cracking in such duty.

A precipitation-hardening chromium-nickel stainless steel which does enjoy high strength and hardness in the hardened condition, along with excellent corrosion-resistance, is the Armco 17-4 PH (about 16.5 percent chromium, about 4.0 percent nickel, about 4.0 percent copper, about 1.0 percent manganese, about 1.0 percent silicon, carbon 0.07 percent max., 0.35 percent columbium, and remainder iron). But, here again, the wear-resisting qualities of the metal leave much to be desired.

A further precipitation-hardening chromium-nickel stainless steel is that described in my prior US. Pat. No. 2,984,563, of May 16, 1961. That steel contains about 12-18 percent chromium, about 13-30 percent nickel, about 36.5 percent silicon, about l-4.5 percent molybdenum, with the sum of the molybdenum and silicon contents being at least 5.5 percent, and remainder iron. While workable and formable, and hardenable by precipitation methods, this steel, too, is lacking in heavy-duty abrasion-resisting properties.

It is perhaps in the straight chromium grades of stainless steel that highest hardness and strength are had, for example, the AISI Types 440A, B and C (about 16-18 percent chromium, about 1.00 percent max. manganese, 1.00 percent max. silicon, 0.75 percent max. molybdenum, with carbon 0.60 percent to 0.75 percent for Type 440A, 0.75 percent to 0.95 percent for Type 4408 and 0.95 percent to 1.20 percent for Type 440C). These steels are hardenable by simple heat-treatment. In hardened condition they are employed in the form of cutlery, surgical instruments, bearings, bushings, fluid valve parts, and the like. Although enjoying good wear-resistance, the steels lack corrosion-resisting qualities. Moreover, the formability of the metal is poor, and it may not readily be fashioned into articles of ultimate use from plate, sheet, strip, and like products. 4

Putting aside the stainless steels, and particularly the austenitic chromium-nickel grades, great hardness and wearresistance are had with the alloy known as STELLITE, an iron-cobalt alloy containing large amounts of chromium and/or tungsten. But this alloy, because of the cobalt requirement as well as the high chromium and/or tungsten requirement, is costly. While suited to applications in the form of high-speed cutting tools, it is not workable as by conversion into plate, sheet, strip, and the like. Actually, the alloy is pretty well confined to use in the form of castings.

A genuine need, therefore, is felt in the art for a corrosionresisting alloy which enjoys a combination of strength and wear-resistance and yet which may be worked and fabricated into desired articles of ultimate use.

SUMMARY OF THE INVENTION Turning now to the practice of my invention, one of the objects is to overcome the deficiencies of the alloys of the prior art as discussed above, and provide an alloy at an acceptable price which not only is corrosion-resisting, but which works well in the hot-mill as in the production of plate, sheet, strip, bar, rod and wire, which lends itself to fabrication as by cutting, threading, tapping, and the like, as well as by welding, and which with simple heat-treatment assures great hardness and resistance to wear, in addition to retaining the desired corrosion-resisting qualities under stress.

My steel essentially consists of the ingredients chromium, nickel, silicon, and one or both of tungsten and molybdenum, with remainder substantially all iron. 1n broad composition, the chromium amounts to about 10 percent to about 22 percent, the nickel about 14 percent to about 25 percent and particularly about 20 percent to about 25 percent, and the silicon about 5 percent to about 12 percent especially about 7 percent to about 1 1 percent. In addition, the steel essentially contains one or more of the ingredients molybdenum up to about 10 percent, tungsten up to about 8 percent, vanadium up to about 5 percent, columbium/tantalum up to about 5 percent, and titanium up to about 5 percent, these additional elements being present in sum total of about 3 percent to about 12 percent. While a best combination of results is had where the sum of the ingredients molybdenum, tungsten, vanadium, columbium/tantalum and titanium is high, good results nevertheless are achieved where the sum of these ingredients and, indeed, the individual ingredients are low or absent, that is, molybdenum is under 5 percent, tungsten is under 3.5 percent, columbium/tantcalum is under 1.5 percent, and both vanadium and titanium are absent, this provided, however, that the silicon content is high, that is, at least about 7 percent. Carbon, of course, is present in amounts up to some 015 percent, preferably not over about 0.10 percent where the silicon content is on the high side. So, too, nitrogen may be present, this in amounts up to some 0.05 percent, preferably not exceeding 0.03 percent. The phosphorus and sulphur contents are low, the phosphorus usually not exceeding about 0.04 percent and the sulphur ordinarily not exceeding about 0.02 percent. Copper in amounts up to 4 percent may be added for special purposes, for example, for improved resistance to sea-water corrosion.

Although the steel may be melted in the vacuum furnace or, indeed, may be melted and then remelted in vacuum, I find that steel of high quality with a minimum of impurities also is had by conventional melting in the electric arc furnace.

The steel, however melted, is readily cast into ingots which for the most part lend themselves to ready conversion in the hot-mill into plate, sheet and strip, bar, rod and wire. Moreover, the steels of the lower silicon contents, say some 5 percent to 7 percent, may be further converted in the coldmill, as in the production of cold-rolled plate, sheet and strip, and in the production of cold-drawn wire. These lower silicon steels may be fabricated as by pressing and bending, as well as machining, that is, cutting, sawing, threading, tapping and the like. And the steel of the higher silicon contents, say some 8 percent to 10 percent, while not readily cold-workable and cold-formable, does lend itself to machining; the steel of the highest silicon ranges, say about 9 percent to about 1 l or 12 percent, although neither cold-workable nor machinable in the ordinary sense, may be hot-worked and, of course, processed by conventional grinding methods.

My steel of all silicon contents is readily weldable, giving a fully austenitic crack-free weld. And, as noted above, the steel is singularly free of impurities, the common impurities carbon, nitrogen and sulphur apparently being rejected by the high silicon content and so, too, the oxides commonly present in many of the stainless steels.

Hardening of the steel is had by first subjecting it to solution-treatment at a temperature of about 2,000 to 2,300 F. and cooling, followed by reheating at some l,200 to 1,500 F. In solution-treated condition the steel has a hardness on the order of Rockwell C50 as a maximum, this ordinarily amounting to about Rockwell B85 for the steel having a silicon content of about percent and Rockwell C50 for the steel with about percent silicon. In the hardened condition there is had a hardness of about Rockwell C72.

While I prefer not to be bound by theoretical explanation, it is my view that in the steel of my invention there are formed molybdenum silicides or tungsten silicides, or perhaps even some complex silicide involving molybdenum, tungsten and chromium. The silicide is of extreme hardness. In the solutiontreated condition the silicides are principally dissolved in the austenitic chromium-nickel matrix. But in the hardened condition, that is, the condition following the hardening heattreatment, these silicides appear in the matrix in finely dispersed form. And when the metal is put into use in hardened condition, much of the matrix wears away, exposing the silicides, with hardness on the order of Rockwell C72, as noted above. It is this fine dispersion of silicides which provides the hard, wear-resisting surface, a surface which is free of binding and galling.

The steel of my invention, because of its surprising combination of strength, corrosion-resistance and resistance to wear by friction, is suited to the production of moving belts and roller chains for food-processing plants. Moreover, I find that the steel is particularly suitable to applications in the petro-chemical industry because of a surprising resistance to sulphidation. It is suited to the production of gears, push-pull controls, fluid valves and even the valves for Diesel engines, because of its surprising resistance to seizing, galling, and the like, in combination with great resistance to wear. Moreover, the steel lends itself to a variety of nuclear applications as in racks, gears and ball screws for positioning the reactor controls. As well, it is suited to the production of pins, bushings, axles, ball-jacks for converting rotary into linear motion or vice versa, and to the production of a variety of threaded assemblies. Additionally, it may be employed in the form of plow points for farm applications, tool bits for oil well drilling and, indeed, a host of applications where there is encountered a combination of frictional wear, along with corrosive attack. It may be employed as a weld-rod for hard-surfacing a product or piece of equipment.

Because of its great hardness, my steel also is suited to the production of cutting blades for a variety of slicing and trimming machines, cutlery, surgical instruments and razor blades. And because of its great hardness at high temperatures and resistance to scaling, the steel is suited to duty in rotary cement kilns as, for example, the chains loosely riding within the kiln to break up the partially decomposed limestone.

DESCRIPTION OF THE PREFERRED EMBODIMENTS While, as noted above, the steel of my invention in broad composition essentially consists of some 10 percent to 20 percent chromium, about l4 percent to about 25 percent nickel, about 5 percent to about 12 percent silicon, with one or more of the ingredients molybdenum up to about 10 percent, tungsten up to about 8 percent, vanadium up to about 5 percent, columbium/tantalum up to about 5 percent and titanium up to about 5 percent, the total of these ingredients amounting to about 3 percent to about 12 percent, and remainder substantially all iron, there are a number of individual embodiments in which there is achieved a best combination of properties for one application or another.

In the steel of broad composition, as well as those of particular preferred embodiment, the amounts of the ingredients chromium, nickel, silicon and the sum total of molybdenum, tungsten, vanadium, columbium-tantalum and titanium are in every sense critical. For with significant departure from the assigned limits, one or more of the desired properties is lost, or seriously suffers. The chromium content must be in the amount of at least about 10 percent, for with a lesser amount there is a distinct loss of corrosion-resistance, and a chromium content exceeding about 22 percent or even about 20 percent, results in a disturbance of the austenitic balance of the metal and some difficulty in forming the desired silicides of molybdenum, tungsten, vanadium, columbium/tantalum and titanium, as well as a sacrifice in workability.

For an assured austenitic structure, the nickel content must amount to at least about 14 percent, better results being had where the nickel content amounts to some l5, l7, 19 or even 20 percent. A nickel content exceeding about 25 percent, however, is inclined to lend such stability to the metal that hardening by heat-treatment becomes difficult, if not virtually impossible. Moreover, hot-workability suffers with excessive nickel, especially where the silicon content is high. For a best combination of results, the nickel content should not exceed about 22 percent, for it is important that there be developed in my steel an austenitic matrix which supports the finely dispersed silicides noted above.

The silicon content of my steel, and its relation to the molybdenum, tungsten, vanadium, columbium/tantalum and titanium content, is particularly critical. For, as pointed to above, I feel that it is a finely dispersed silicide of one or more of these latter ingredients, which may even include some chromium, which assures the surprising resistance to wear which is enjoyed by my steel. The silicon content in my view should not be less than about 7 percent, certainly not less than about 5 percent, in order to assure resistance to wear and abrasion. On the other hand, the silicon content should not exceed about 12 percent, for otherwise hot-workability drastically suffers. Actually, a silicon content of about 5% to some 6 or 7 percent is required in order to assure reasonably good cold-working properties, a silicon content of some 7 percent to 9 percent although suffering a loss of cold-formability nevertheless possesses good machining properties; and a silicon content of some 9 to ll or 12 percent for maximum resistance to wear and abrasion and a cutting edge of maximum life. While it reasonably might be expected that the high silicon content in combination with the high chromium and molybdenum or tungsten or vanadium or columbium-tantalum or titanium contents would result in a steel of martensitic structure, it seems that those elements interfere with the ferritizing effect of the silicon. Regardless of explanation, the steel is austenitic and non-magnetic; microscopic examination fails to reveal the presence of ferrite.

The sum of the molybdenum, tungsten, vanadium, columbium/tantalum and titanium contents of my steel should be at least about 3 percent in total, for otherwise there is insufficient potential for adequate formation of the required silicides; preferably both molybdenum and tungsten are employed, or as desired both molybdenum and vanadium or molybdenum and columbium/tantalum may be used, for with the combination of the special alloying ingredients it appears that there is a synergistic effect which not only assures maximum wear but also a maximum assured freedom from sticking, seizing, or galling between contacting surfaces of the same or another metal. But the molybdenum content, where employed, should not exceed about l percent and the tungsten content should not exceed about 8 percent, with the sum of the molybdenum and tungsten contents not exceeding about 8 percent, certainly not exceeding some 10 or 12 percent, for with an excess, the hot-working properties are lost and so, too, the machinability. Actually, with the sum of the molybdenum, tungsten or other alloying ingredients exceeding about 7 or 8 percent, there is little added benefit over that had where the sum total of these ingredients amounts to some 6 or 7 percent.

ln my steel neither carbon nor nitrogen is required; the high silicon content appears to reject these two ingredients and assure metal free from impurity and of maximum cleanliness.

Now of the preferred embodiments of my invention, one steel essentially consists of about 10 percent to about 20 percent chromium, about 14 percent to about 20 percent nickel, about percent to about 12 percent silicon, about 3 percent to about 9 percent molybdenum, or, as desired, about 2 percent to about 4 percent each of molybdenum and tungsten, with remainder substantially all iron. Another essentially consists of about 14 percent to about 16 percent chromium, about 15 percent to about 19 percent nickel, about 5 percent to about 7 percent silicon, with up to about 5 percent each of molybdenum and tungsten in total amount of about 3 percent to 8 percent, more particularly about 2 percent to about 4 percent molybdenum and about 2 percent to about 4 percent tungsten, and remainder substantially all iron. These steels may contain columbium up to about 5 percent, particularly about 0.2 percent to about 2 percent columbium, the columbium forming a silicide of great hardness. They lend themselves to cold-reductions up to about 60 percent. They are fully austenitic in the annealed or solution-treated condition. They may be fabricated as by cutting, drilling, threading, and the like. And they readily may be welded. They are suited to a variety of applications where a combination of corrosion-resistance and resistance to frictional wear is required. The steel also is suited for duty as an internal combustion engine valve. The low density of the metal because of the high silicon content assures a minimum of inertia; low inertia is important to the rapid reciprocation encountered in valve operation. And the high hot-hardness enjoyed by my steel is a further benefit. Moreover, the high hot-hardness and the retention of this hardness at high temperatures, say up to 1,700 E, makes the steel especially suited to duty as tools and dies for the forming of titanium and titanium alloys. In such applications the temperatures may well reach some l,200 to 1,400" P.

A further preferred steel according to my invention essentially consists of about 19 percent to about 22 percent chromium, about 20 percent to about 25 percent nickel, about 5 percent to about 7 percent or even about 7 percent to about 1 1 percent silicon, with one or both of molybdenum and tungsten each in amounts up to about 5 percent and the total amounting to about 3 percent to 8 percent, and remainder substantially all iron. The steel of this embodiment is particularly resistant to corrosion and to wear. Here again, columbium may be present up to about 2 percent.

Another embodiment essentially consists of about 10 percent to about 18 percent chromium, about 17 percent to about 20 or 22 percent nickel, about 5 or 7 percent to about 9 percent silicon, about 2 percent to about 4 percent molybdenum with tungsten up to about 5 percent, or molybdenum up to about 5 percent and tungsten about 2 percent to about 4 percent, and remainder substantially all iron. In this steel columbium may be added in amounts up to about 2 percent. A more specific preferred steel essentially consists of about percent chromium, about 18 percent nickel, about 8 percent silicon, with about 3 percent molybdenum and tungsten in combination, and remainder substantially all iron. In the steel of this embodiment, both broadly and specifically, great hardness and resistance to wear are had. The steel, although not workable by the usual methods, is readily machinable into a host of articles of ultimate use where particular resistance to wear is required in addition to resistance to corrosion. The exceptional hot-hardness of this steel makes it particularly suited to duty as a valve for Diesel engines, where there are reached operating temperatures of 1 ,600 F.

Perhaps the particular steel in which there is enjoyed a greatest resistance to wear essentially consists of about 10 percent to about 16 or 18 percent chromium, about 17 percent to about 22 percent nickel, about 7 percent to about 1 1 percent silicon, about 1 percent to about 5 percent molybdenum and about 1 percent to about 5 percent tungsten with the sum total of the two amounting to about 3 percent to 8 percent, and remainder substantially all iron. This steel not only enjoys a maximum of wear resistance, with a maximum freedom from seizing or galling, along with good resistance to corrosion, making it suitable to a variety of applications where this combination of properties is called into play, but it also takes a keen cutting edge of long retained sharpness, making it particularly suitable for cutlery, razor blades, surgical instruments and the cutting blades of food-processing equipment. I feel that the effectiveness of the cutting edge is heightened by the circumstance that there is a fine dispersion of extremely hard particles, the silicides, as noted above, which in effect give a very fine serrated edge. Because of its great hardness the steel also is beneficially employed as machine tools, as for example, those suited to cutting stainless steel.

Other preferred steels essentially consist of about 10 percent to about 22 percent chromium, about 14 percent to about 20 percent nickel, about 5 percent to about 1 1 percent especially about 7 percent to about 11% silicon, about 2 percent to about 9 percent molybdenum, about 1 percent to about 5 percent vanadium, and remainder substantially all iron. A further steel essentially consists of about 10 percent to about 22 percent chromium, about 14 percent to about 20 percent nickel, about 7 percent to about ll percent silicon, about 2 percent to about 9 percent molybdenum, about 1 percent to about 5 percent columbium/tantalum, and remainder substantially all iron. A still further steel essentially consists of about 10 percent to about 22 percent chromium, about 14 percent to about 20 percent nickel, about 5 percent to about 11 percent particularly about 7 percent to about 1 1 percent silicon, about 2 percent to about 9 percent molybdenum, about 1 percent to about 5 percent titanium, and remainder substantially all iron. In these steels carbon is present in amounts up to about 0.10 percent. All are possessed of great hardness when solution-treated and then hardened by reheatmg.

As particularly illustrative of the steel of my invention, I give below in Table 1(a) the analyses of some twelve steels, two according to the invention and ten not answering to the compositional requirements of my steel. In Table l(b) 1 set out the heat-treatment given the various steels of Table 1(a), the hardness of these steels, and the results of the wear-resisting tests conducted on the same.

TABLE I (a) [Chemical composition of twelve stainless steels] Percent Heat Number C Si Cr Ni Cu M0 W Ch Steels according to the invention.

The comparative wear-resisting qualities of the. steels of Table 1(a) are presented below in Table 1(b). The wear tests were made on a Falex Lubricant Tester advertised by the National Tube Division of the United States Steel Corporation. It employs a fit-HP motor which vertically rotates a test sample in the form of a pin at the constant speed of 290 RPM. The test samples were located between two V-blocks which exerted a controlled lateral or jaw pressure amounting to some 400 or 500 pounds. The time of test, in absence of sample failure, was set at 1 minute. For each steel there was tested a set of four specimens, and it is the average results which are recorded.

TABLE I(b) [Wear test results and hardness of the steels of Table 1(a)] Heat Rockwell Number Hardening treatment hardness Wear results 12-6413. 1,400 F.16 hrs.W.Q RC 35.0 Excellent. R-6414 do RC 20.5 D0. R6415 1,400 F.-50 hrs.-A.C RC 52.5 Samples broke in test. 11-6416 do RC 53.5 l)o. R6417 1,400 F. hl'S.-W.Q RC 28.0 P001. R-6418 do R11 88.0 Poor and seized. 11-6419 do B13920 Poor and seized heavily. 11-6420 d0 RB 85.5 D0. R6631 Tested as received. Very poor ulul heavy seizing. Do. Do. 1):).

Steels according to the invention.

The two high-silicon steels of my invention R-6413 and R-6414, with a jaw pressure of 500 pounds, well survived the 1-minute test. Both steels, as a result of the friction encountered, glowed red-hot after a few seconds, reaching a temperature of some l,600 F. In spite of the high temperatures encountered, however, there was no evidence of seizing. While there was some discoloration of the specimens of these steels, it was but slight. The results indicate superior wear-resisting characteristics, characteristics in no way approached by the other steels tested.

Although the low-silicon, high-chromium steels R-64 l 5 and R-64 l 6 were extremely hard, they also were very brittle. And while they did not seize heavily in test at 500 pounds pressure, upon getting hot, they tended to grab, causing an impact load with resulting shear of specimen. Although the wear-resisting qualities were good, the extreme hardness and tendency to grab when hot make these steels unsuited to many applicatrons.

While the low-silicon, high-molybdenum steels R-6417 and R-6418 showed wear almost immediately, even when the jaw pressure was reduced from 500 pounds to 400 pounds, the specimens of R-6417 showed no evidence of seizure. The steel R-64l8, however, experienced a considerable amount of seizure, two of the four specimens binding up completely. The wear of all was excessive.

The high-columbium steels R-64l9 and R-6420 seized heavily, seizing occurring with a jaw pressure of only some 350 to 400 pounds. Moreover, the wear-resisting qualities were poor. The chromium-nickel-copper precipitationhardening steels R-663l, R-6632, R-6633 and R-6634, whether of low or of high columbium contents, evidenced heavy seizing similar to the R-64l9 and R-6420 steels, and particularly poor wear-resisting qualities. It is only the steel of my invention which is characterized by a substantial freedom from seizure even when red-hot, along with good resistance to wear and freedom from brittleness.

Twenty-one further austenitic chromium-nickel steels according to my invention in which there is employed a silicon content of at least 5 percent, and for best results some 7 percent and more, are set out below in Table ll(a). These steels, in addition to the chromium, nickel and silicon contents, include one or more of the ingredients molybdenum, tungsten, vanadium, columbium/tantalum, titanium, and even copper. The hardnesses and the wear-resisting qualities of these steels are presented in Table ll(b).

TABLE ll(a) [Chemical composition of twenty-one further steels according to the invention] lnruenl.

lleut number (1 Si (1 Ni Mn (71) W Other 7. 88 14.02 18. 50 7. 82 14. 07 18.30 1 l. 01 7. 74 14. 71 18. 28 3. 01 ll. 06 14. 58 18. .22 2. 04

NOTE. Manganese 0.61% max. phosphorus 0.016% mnx., sulfur 0.014';Y;. max., nitrogen 0.05% max.

The hardnesses of the steels of Table ll(a) are presented below in Table ll(b), both-for the annealed or solution-treated condition of the metal and for the hardened condition. Solution-treatment was had by heating at 2,000 E. for 30 minutes and cooling in air. And hardening was achieved by reheating at l,500 F. for 16 hours and air cooling. The hardness figures are given in Rockwell C or B, as the case may be. All steels were found to possess excellent wear-resisting qualities, as determined by test according to the method employed for the steels of Table 1(a) as shown in Table 1(b).

TABLE ll(b) Wear Test Results and Hardness of the Steels of Table ll(a) Solution-Treated Hardened Wear Heat No. Condition Condition Results R 7107 C 25 C 45 Excellent R 7108 C 24 C 42 Excellent R 7109 C 27 C 46 Excellent R 7172 C 40 C 55 Excellent R 7173 C 38 C 52 Excellent R 7174 C 51 C 66 Excellent R 7175 C 55' C 72 Excellent R 7444-3 C 22 C 41 Excellent R 7556-3 C 23 C 43 Excellent R 7557-3 C 25 C 46 Excellent R 7606 B C 27 Excellent R 7607 C 21 C 37 Excellent R 7608 C 22 C 32 Excellent R 7609 C 22 C 36 Excellent R 7610 B 98 C 29 Excellent R 7611 C 21 C 36 Excellent R 7659 C 33 C 48 Excellent R 7660 C 34 C 52 Excellent R 7661 Y C 34 C 54 Excellent R 7662 C 32 C 46 Excellent R 7663 C 35 C 44 Excellent In studying the hardness of the several steels presented in Table ll(b) of the differing compositions set out in Table ll(a), attention is drawn to the synergistic effect achieved with the combination of molybdenum and tungsten, also that had with the combination of molybdenum and vanadium, and even that had with the combination of molybdenum and titanium.

More particularly, for the steels having a molybdenum content of about 3.5 percent (Heat Nos. R 7107 and R 7108), the hardness in the hardened condition amounts to some Rockwell C42/45. With about 4 percent molybdenum (Heat No. R 7659), it comes to Rockwell C48. And with about 8 percent molybdenum (Heat No. R 7660), it comes to about Rockwell C52. Similarly, for the steels with about 6 percent tungsten (Heat Nos. R 7444-3, R 75563 and R 7557-3), the hardness figures are Rockwell C 41/46. Where molybdenum and tungsten both are present, the one amounting to about 3 percent and the other about 2 percent, with the sum of the two coming to about 5 percent (Heat Nos. R 7172, R 7173, R 7174 and R 7175), the hardness comes to Rockwell C 52/55 where the silicon content is on the order of 9 percent (Heat Nos. R 7172 and R 7173), and Rockwell C 66/72 where the silicon amounts to about 1 1 percent (Heat Nos. R 7174 and R 7175). Where the silicon content is less than about 8 percent, little benefit seems to be had as a result of the presence of both molybdenum and tungsten in sum total amounting to about 5 percent (Heat No. R 7109, with a hardness of only Rockwell C 46).

Similarly, the steel containing both molybdenum and vanadium in total amount of about 4.5 percent (Heat No. R 7607) enjoys a hardness or Rockwell C 37, whereas with vanadium alone in like amount (about 4 percent for Heat No.

'R 7606) the hardness is only Rockwell C 27. The other ingredients are virtually the same for the two steels, the silicon amounting to less than 7 percent. Where molybdenum and vanadium are present in total amount of about 7 percent (Heat No. R 7662), there is had a hardness or Rockwell C 46, the silicon here amounting to about 8 percent. This steel is particularly suited to applications involving frictional wear, as in a piston-cylinder relationship. It is suited to the production of a variety of actuators for servo-mechanisms.

The steels with columbium (Heat No. R 7608) and with titanium (Heat No. R 7610) are characterized by hardnesses of Rockwell C 32 and C 29 respectively. With molybdenum in addition there is some increased hardness, but this is rather slight; the hardness for both of the molybdenum-bearing steels is Rockwell C 36. The silicon content of all four of these steels is about the same, namely, just under 6 percent. Where the total of the molybdenum and titanium additions is increased to about 7 percent and the silicon is about 8 percent (Heat No. R 7663), the hardness is raised to some Rockwell C 44. The columbium/tantalum-containing steels, as well as the titanium-bearing steels, are especially suited to hard-surfacing applications, that is, applications where the steels are remelted and sprayed onto various pieces of apparatus and equipment to serve as an effective hard and abrasion-resistant surface.

It rather clearly appears that maximum hardness is realized in the steel employing the two ingredients molybdenum and tungsten in combination and in total amount of about 5 percent, with silicon on the order of about 11 percent, as more particularly pointed to above. Such a steel is especially suited to heat-hardened articles of great hardness and wear-resistance, notably articles and equipment for engaging in frictional wear and those employed as cutting tools.

In conclusion, it will be seen that 1 provide in my invention an alloy, more particularly an austenitic stainless steel, in which there are achieved the various objects set out above and in which there are had the various advantages described. The steel of my invention not only is resistant to corrosion in the presence of chlorides, brines, sulphides and other acids and salts commonly encountered in the food-processing, the petro-chemical and earth-moving industries, but is resistant to the seizing, galling and wear encountered in actual use. The steel lends itself to mechanical fabrication and welding in the production of a wide variety of articles, products, equipment and apparatus.

Since many possible embodiments may be made of the alloy of my invention, and since many changes may be made in the particular embodiments set out above, it is to be understood that all matter described herein is to be interpreted as illustrative and not by way of limitation.

I claim:

1. Austenitic stainless steel precipitation-hardenable to great hardness and wear-resistance essentially consisting of about 10 percent to about 20 percent chromium, about 14 percent to about 20 percent nickel, about 7 percent to about 12 percent silicon, about 2 percent to about 4 percent molybdenum, about 2 percent to about 4 tungsten, carbon not exceeding 0.15 percent and remainder substantially all iron.

2. Austenitic stainless steel precipitation-hardenable to great hardness and wear-resistance essentially consisting of about 10 percent to about 18 percent chromium, about 17 percent to about 19 percent nickel, about 7 percent to about 9 percent silicon, about 3 percent to about 7 percent molybdenum, carbon not exceeding 0.15 percent and remainder substantially all iron.

3. Austenitic stainless steel precipitation-hardenable to great hardness and wear-resistance essentially consisting of about 10 percent to about 20 percent chromium, about 14 percent to about 20 percent nickel, about 5 percent to about 12 percent silicon, about 7 percent to about 10 percent molybdenum, carbon not exceeding 0.15 percent and remainder substantially all iron.

4. Austenitic stainless steel precipitation hardenable to great hardness and wear-resistance essentially consisting of about 10 percent to about 22 percent chromium, about 14 percent to about 25 percent nickel, about 5 percent to about 11 percent silicon, about 3.5 percent to about 8 percent tungsten, up to about 7 percent molybdenum, carbon not exceeding 0. 15 percent and remainder substantially all iron.

5. Austenitic stainless steel essentially consisting of about 10 percent to about 22 percent chromium, about 14 percent to about 25 percent nickel, about 5 percent to about 12 percent silicon, about 1 percent to about 5 percent vanadium, up to about 10 percent molybdenum, carbon not exceeding 015 percent and remainder substantially all iron.

6. Austenitic stainless steel precipitation-hardenable to great hardness and wear-resistance essentially consisting of about 10 percent to about 20 percent chromium, about 15 percent to about 20 percent nickel, about 5 percent to about 11 percent silicon, up to about 9 percent molybdenum, about 1.5 percent to about 4 percent columbium, carbon not exceeding 0. 15 percent and remainder substantially all iron.

7. Austenitic stainless steel essentially consisting of about 10 percent to about 22 percent chromium, about 14 percent to about 25 percent nickel, about 5 percent to about 12 percent silicon, about 1 percent to about 5 percent titanium, up to about 10 percent molybdenum, carbon not exceeding 015 percent and remainder substantially all iron.

8. Austenitic stainless steel precipitation-hardenable to great hardness and wear-resistance essentially consisting of about 10 percent to about 18 percent chromium, about 17 percent to about 22 percent nickel, about 9 percent to about 11 percent silicon, about 2 percent to about 4 percent molybdenum, up to about 5 percent tungsten, carbon not exceeding 0.15 percent and remainder substantially all iron.

9. Austenitic stainless steel precipitation-hardenable to great hardness and wear-resistance essentially consisting of about 10 percent to about 18 percent chromium, about 19 percent to about 22 percent nickel, about 9 percent to about 1 1 percent silicon, up to about 5 percent molybdenum, about 2 percent to about 4 percent tungsten, carbon not exceeding 0.15 percent and remainder substantially all iron. 

2. Austenitic stainless steel precipitation-hardenable to great hardness and wear-resistance essentially consisting of about 10 percent to about 18 percent chromium, about 17 percent to about 19 percent nickel, about 7 percent to about 9 percent silicon, about 3 percent to about 7 percent molybdenum, carbon not exceeding 0.15 percent and remainder substantially all iron.
 3. Austenitic stainless steel precipitation-hardenable to great hardness and wear-resistance essentially consisting of about 10 percent to about 20 percent chromium, about 14 percent to about 20 percent nickel, about 5 percent to about 12 percent silicon, about 7 percent to about 10 percent molybdenum, carbon not exceeding 0.15 percent and remainder substantially all iron.
 4. Austenitic stainless steel precipitation hardenable to great hardness and wear-resistance essentially consisting of about 10 percent to about 22 percent chromium, about 14 percent to about 25 percent nickel, about 5 percent to abouT 11 percent silicon, about 3.5 percent to about 8 percent tungsten, up to about 7 percent molybdenum, carbon not exceeding 0.15 percent and remainder substantially all iron.
 5. Austenitic stainless steel essentially consisting of about 10 percent to about 22 percent chromium, about 14 percent to about 25 percent nickel, about 5 percent to about 12 percent silicon, about 1 percent to about 5 percent vanadium, up to about 10 percent molybdenum, carbon not exceeding 0.15 percent and remainder substantially all iron.
 6. Austenitic stainless steel precipitation-hardenable to great hardness and wear-resistance essentially consisting of about 10 percent to about 20 percent chromium, about 15 percent to about 20 percent nickel, about 5 percent to about 11 percent silicon, up to about 9 percent molybdenum, about 1.5 percent to about 4 percent columbium, carbon not exceeding 0.15 percent and remainder substantially all iron.
 7. Austenitic stainless steel essentially consisting of about 10 percent to about 22 percent chromium, about 14 percent to about 25 percent nickel, about 5 percent to about 12 percent silicon, about 1 percent to about 5 percent titanium, up to about 10 percent molybdenum, carbon not exceeding 0.15 percent and remainder substantially all iron.
 8. Austenitic stainless steel precipitation-hardenable to great hardness and wear-resistance essentially consisting of about 10 percent to about 18 percent chromium, about 17 percent to about 22 percent nickel, about 9 percent to about 11 percent silicon, about 2 percent to about 4 percent molybdenum, up to about 5 percent tungsten, carbon not exceeding 0.15 percent and remainder substantially all iron.
 9. Austenitic stainless steel precipitation-hardenable to great hardness and wear-resistance essentially consisting of about 10 percent to about 18 percent chromium, about 19 percent to about 22 percent nickel, about 9 percent to about 11 percent silicon, up to about 5 percent molybdenum, about 2 percent to about 4 percent tungsten, carbon not exceeding 0.15 percent and remainder substantially all iron. 